1. Field of the Invention
This invention relates to a device for detecting failure of an ultrasonic apparatus which utilizes ultrasonic pulses for the detection of, for example, an obstruction.
2. Description of the Prior Art
An ultrasonic apparatus commonly employed for the detection of an obstruction comprises an ultrasonic pulse generator generating a pulse signal entrained on a carrier and an ultrasonic pulse transmitter transmitting ultrasonic pulses by receiving the pulse signal from the generator. The normal or trouble-free operation of the ultrasonic pulse transmitter in such an ultrasonic apparatus has been confirmed by an ultrasonic pulse receiver which receives a direct ultrasonic pulse. The prior art failure detecting device has therefore been defective in that a receiver is inevitably required for the confirmation of the trouble-free operation of the transmitter, and the apparatus itself cannot confirm the operation of the transmitter.
In another prior art ultrasonic apparatus utilizing ultrasonic pulses for checking a normal operation, a receiving circuit associated with a circuit required for the transmission of ultrasonic pulses detects the time difference between the time of reception of a direct pulse and the time of reception of a reflected pulse. The operation of the device for confirming the normal or trouble-free operation of the ultrasonic apparatus has been such that a display unit displays the trouble-free operation of the entire apparatus when the receiving circuit receives a direct pulse at the time at which the confirmation is required. However, the prior art failure detecting device has a disadvantage in that, in order to receive the direct pulse for the purpose of confirmation of the trouble-free operation, a dead time zone must be provided for distinguishing the direct pulse from the reflected pulse.